1. Field of the Invention
This invention relates to the hydraulic conductivities of liquids through permeable materials and particularly relates to the conductivity of water through earth. It also relates to testing such conductivity from the surface of the earth to great depths beneath the surface and above the water table while preventing contamination by falling soil and debris. It more particularly relates to instruments that establish a static head of water within a borehole and maintain the water at this predetermined level by use of a float and valve system. It specifically relates to a highly versatile permeameter having a float and valve system that provides a mechanical advantage enabling use of the permeameter at any selected depth up to such great depths.
2. Review of the Prior Art
It is often important to estimate the hydraulic conductivities of porous materials, such as various types of earth, for solving many agricultural, hydrological, and environmental problems. In a practical sense, these conductivities are needed in order to safely and economically develop lands for urban and agricultural uses. Hydraulic conductivity values are also important considerations in design and construction of building and roadway foundations, on site sewage wastewater treatment systems, and storm water infiltration facilities. These hydraulic conductivity values are important for design of constructed wetlands and for estimating the rate of transport of liquid contaminants from waste disposal sites and leaking storage tanks. Hydraulic conductivity values are additionally important in design of irrigation systems and drainage of agricultural lands.
Soil hydraulic conductivity can be used to describe the ability of earthen materials to transmit water. Darcy's Law describes the relationship of the volume of water, moving through a cross sectional area of soil (commonly known as flux) along the hydraulic gradient of the water flow path, to the hydraulic conductivity. Under saturated conditions, such as below a water table, hydraulic conductivity is referred to as saturated hydraulic conductivity. Even though Darcy's law was originally developed to describe saturated flow, the principles of the law can be applied to water movement in partially saturated soils above the water table.
The determination of hydraulic conductivity under field conditions can be complicated because of the natural variation of soil properties and the specific need for which the test is being conducted. Soils typically contain multiple contrasting layers and often exhibit significantly differing hydraulic conductivity values along preferential flow paths within the soil matrix.
Prior art instruments developed for measuring hydraulic conductivity of soils above the water table in the field have generally fallen into three groups. The first group introduces either a ponded static (i.e., constant) or a variable (i.e., falling) head of water into the bottom of an unlined borehole below the ground surface or into a confining ring in contact with the ground surface. Instruments that establish a static head of water within a borehole maintain the water at a predetermined level, usually by use of either a float and valve system or a marriotte tube system. The rate of water flow necessary to maintain a constant water level in the borehole at the predetermined level is utilized to estimate hydraulic conductivity of the soil.
Methods used to measure the saturated hydraulic conductivity in a borehole utilizing a constant head of water have been referred to as the shallow well pump-in technique or constant-head well permeameter. Instruments in this first group that utilize a falling head procedure usually measure the drop of water from a predetermined level in a lined or unlined borehole as it dissipates into the soil to estimate hydraulic conductivity.
The second group of instruments applies water through a semi-permeable membrane to a soil surface, which is under negative pressure (tension), to measure unsaturated hydraulic conductivity. The third group of instruments utilizes various methodologies, which include electrical resistivity procedures and gas or liquid injection into the soil through penetrating probes. The instruments in the third group typically require a power source, fluid or gas pumps, multiple chambers, borehole packers, electronic data loggers, and/or complex analysis procedures.
U.S. Pat. No. 6,212,941 of G. Cholet describes a permeameter, designed particularly for measuring the air permeability of cigarette paper, which comprises a measuring head having two chambers opening onto two sides of a test piece, one of these chambers being connected to a measuring circuit successively comprising at least one flow meter and a pumping means capable of generating pressure or a partial vacuum in the circuit, an adjusting means for maintaining the circuit at a given pressure, and an electronic circuit comprising plural calibrated amplifiers having inputs connected to the output of the flowmeter and outputs connected to the inputs of a multiplexer whose output is connected to a processor via an analog-to-digital converter.
U.S. Pat. No. 6,178,808 of X. Wang et al relates to a method for measuring hydraulic conductivity of geological samples, using a closed volume pumping system that ensures constant volume of test liquid within the sample and a shaped tube of mercury to provide a constant pressure difference across the sample for eliminating second order influences on the hydraulic conductivity measurement and to speed measurement.
U.S. Pat. No. 6,105,418 of T. Kring discloses a constant-head float valve assembly which includes a J-shaped fluid conduit for intermittently delivering water from a supply container to a borehole. As the float moves downward with dissipating water levels, a shutoff valve is contacted and thereby opened to replenish the water in the borehole. The rising water moves the float upward and away from the valve, thereby allowing pressure of the incoming water to close the valve again.
U.S. Pat. No. 6,098,448 of W. Lowry et al describes an apparatus and method for discrete soil gas and saturated liquid permeability measurements with direct push emplacement systems, such as a cone penetrometer rod. Gas or liquid is injected into the soil at a predetermined location of the penetrometer rod after such a system, having at least one injection port and at least two measurement ports, has penetrated the soil to a predetermined depth. A pressure response is recorded from each measurement port, which is at a known distance from the injection port on the same penetrometer rod, thereby providing differential pressure response data allowing calculation of the soil permeability directly by using a one-dimensional, spherical, steady-state, porous flow model to measure the effective permeability of the soil, without substantially disturbing the surrounding soil.
U.S. Pat. No. 4,561,290 of Jewell utilizes a float valve assembly, connected to a water supply reservoir, to regulate water inflow and obtain a constant water level within a borehole. The float responds to a rising water level by regulating water flow through a valve and thereby maintaining a constant water level as the water in the test bore percolates away from the bore through the soil around it at a steady rate.
U.S. Pat. No. 6,055,850 of D. Turner et al describes a multi-directional permeameter comprising a mold which is removably secured to a base and having a removably secured lid. A porous plate circumferentially disposed around the midsection of the mold and another porous plate at its bottom are connected to the interior of the mold by filter papers. The interior of the mold is filled with a soil sample to be tested. This soil sample may be selectively compressed. Water is introduced above the soil sample through an inlet port. After percolation through the soil, the filter papers, and the porous plates, the water leaves through drainage ports, whereby the coefficients of permeability of the soil sample may be determined either horizontally, vertically, or simultaneously horizontally and vertically.
U.S. Pat. No. 5,520,248 of J. Sisson et al discloses an apparatus for determining the hydraulic conductivity of an earthen material. This apparatus comprises: a) a semipermeable membrane having a fore earthen material bearing surface and an opposing rear liquid receiving surface; b) a pump connected to the semipermeable membrane rear surface and capable of delivering liquid to the membrane rear surface at a plurality of selected variable flow rates or at a plurality of selected variable pressures; c) a liquid reservoir connected to the pump and containing a liquid for pumping to the membrane rear surface; and d) a pressure sensor connected to the membrane rear surface to measure pressure of liquid delivered to the membrane by the pump which preferably comprises a pair of longitudinally opposed and aligned syringes operated so that one syringe is filled while the other is simultaneously emptied.
U.S. Pat. No. 5,161,407 of M. Ankeny et al relates to a soil desorption device and method utilizing a pressure cell which contains soil samples, the pressure cells being attachable to pneumatic pressure manifolds and selectively being independently valved. The cells may be connected to collection containers for any desorbed fluid. Each cell utilizes a cylindrical container having rubber gaskets at opposite ends thereof for sealable attachment of top and bottom plates. A thin nylon membrane having small pores is positioned at the bottom of the container, and the bottom plate has apertures, whereby fluid forced through the membrane can pass to fluid collection devices.
U.S. Pat. No. 4,984,447 of J. Phillips describes a soil testing apparatus having a hollow shaft for insertion into a test hole. The shaft includes vertically adjustable wedging blades for centering alignment in the test hole. A hand pump evacuates water from the test hole to a predetermined null point, whereupon vertical movement of a float and float rod supported and guided within the shaft over a finite period of time yields a direct percolation absorption rate.
U.S. Pat. No. 4,884,436 of M. Ankeny et al discloses an automated tension infiltrometer having a soil contacting base to which a porous plate is attached for interfacing the infiltrometer with the soil to be analyzed. A Marriotte column is positioned in the base so that its open bottom end abuts the porous plate, and a bubble tower is also positioned in the base with a bubbling tube operatively connecting its interior and the interior of the Marriotte column. The bubble tower is adjustable to provide variable tension to the Marriotte column. Pressure changes in the upper and lower parts of the Marriotte column are continuously measured by first and second transducers while water from the column infiltrates into the soil.
U.S. Pat. No. 4,829,817 of L. Koslowski describes an apparatus for taking soil percolation tests which comprises a threaded shaft having a plurality of marking discs that can be selectively positioned along the shaft at predetermined gradations, a positioning brace that overlies the shaft for securing the shaft in vertical alignment, a mounting disc affixed near a base end of the shaft that becomes flush with the soil when the shaft is inserted into a percolation test hole, and a receiving disc near a top end of the shaft for receiving the positioning brace as it straddles the test hole.
U.S. Pat. No. 4,561,290 of D. Jewell discloses a float valve apparatus for soil percolation measurements. This apparatus comprises a float valve assembly, integral with a water supply system, which responds to changes in a predetermined water level inside a test bore to regulate water flow through the float valve into the bore to maintain this water level. The float valve assembly is positioned at different depths below ground level by suspension at the lower end of a premarked flexible hose hanging freely inside the test bore. The float valve housing is open at its lower end so that water around it in the test bore can raise the float therewithin to throttle the water flowing down through a reducer at the end of the hose and directly above the float. After an initial transient stage, the water in the test bore percolates away from the bore through the soil around it at a steady rate.
U.S. Pat. No. 4,520,657 of H. Marthaler discloses an apparatus for determining the pressure of capillary water in soil, comprising a probe tube and a pressure measuring device that measures pressure by means of an elastically deformable membrane. The probe tube is closed and pneumatically coupled to the pressure measuring device by a pierceable and self-sealing closure member. A hollow needle suitable for piercing the closure member is attached to the pressure measuring device. Mechanical-electrical transducers measure the pressure corresponding to the deformation of the membrane.
U.S. Pat. No. 4,341,110 of P. Block relates to a percolation testing apparatus for automatically recording the rate of fluid absorption of the soil surrounding a test hole. This apparatus includes three subsystems: a) a tubular housing having a plurality of perforations at its lower end; b) a float subassembly which includes a float member, a float rod, and a channel-shaped float rod extension; and c) a clock-marker subassembly which includes a guide member for the channel extension of the float rod. During a test procedure the rate of descent of a float is recorded on a tape by a timer controlled marker.
U.S. Pat. No. 4,182,157 of R. Fink describes a soil percolation testing apparatus comprising an elongated guide rod having one end to be driven into the bottom of a test hole for supporting a rod along which a gauge rod is slidable by means of guide brackets on the gauge rod and a scale strip which is attached to the upper end of the gauge rod for vertical movement relative to a reference marker supported adjustably upon the upper portion of the guide rod. A float is connected to the lower end of the gauge rod for vertical floating movement in the test hole that moves the scale strip relative to the reference marker which is stationary on the guide rod.
In U.S. Pat. No. 3,954,612, A. Wilkerson disclosed septic tank systems buried below the ground level and having a cover to minimize rainwater soaking into its drainage bed. The gravel-filled ditch is then covered with dirt. An indicator above the ground surface shows the water level in tributaries so that excess liquid can be pumped out before upstream sewage is backed up.
In U.S. Pat. No. 3,926,143, H. Hothan describes an upright gauge that detects and gives visual indications of the presence of free water at a predetermined depth in the ground. The gauge has a tubular housing in which a spherical float, with an attached float stem, is enclosed. Water applied to the nearby soil enters the gauge, moves the float upwardly, and causes the stem to rise and signal water penetration of the soil.
In U.S. Pat. No. 3,892,126 of J. Curtin, a test hole in soil is filled with a predetermined amount of liquid and has a calibrated measuring stick extending up from a support member having a float member disposed in the liquid to indicate up and down movement of the liquid level.
In U.S. Pat. No. 2,949,766, D. Kirkham et al describe an annular water reservoir which has an inlet tube as its inner wall that enters the ground. Water is in the annular space, and a graduated cylinder that fits within the annular space is inverted and suspended by its content of air, thereby maintaining a constant pressure. As air enters the soil, the float falls accordingly.
In an article published in Soil Science Society of America Journal, Vol. 53, No. 5, pp. 1356–1361, Sept.–October 1989, by A. Amoozegar, entitled “A Compact Constant-Head Permeameter for Measuring Saturated Hydraulic Conductivity of the Vadose Zone”, a compact constant-head permeameter is described for maintaining a constant height of water (>5 cm) at the bottom of a 4- to 10-cm-diameter hole in the unsaturated zone, and measuring the amount of water flowing into the hole, thereby measuring KS from the soil surface to a depth of two meters.
In another article published in the same issue of the same journal, pp. 1362–1367, by A. Amoozegar, entitled “Comparison of the Glover Solution with the Simultaneous-Equations Approach for Measuring Hydraulic Conductivity”, the Glover solution and the simultaneous-equations approach for determining the saturated hydraulic conductivity (KS) of the vadose zone by the constant-head well permeameter technique are examined. The uncertainty associated with calculating KS by the simultaneous-equations approach, as compared with using the Glover solution, is then discussed.
However, neither of these devices incorporates an apparatus for magnifying the vertical force of the float body that is necessary for valve regulation at large depths and flow volumes, nor do they incorporate a backflow check valve to prevent incident entry of suspended soil particles and other contaminates into the float chamber. In addition, neither of these devices includes a means for eliminating the entry of contaminants through its air equalizing passage into the interior of the device.
Soil hydraulic conductivity has been historically measured on a smaller scale in the laboratory, utilizing a falling or constant head of water applied to soil core samples retrieved from the field or on remolded soil samples. Laboratory centrifugal force methods are also utilized to estimate hydraulic conductivity. Laboratory measurements are often significantly at variance with in situ field measurements because of the differing methodologies and the inherent difficulty of obtaining undisturbed soil samples and replicating natural environmental and stress conditions in the laboratory.
It is desirable to have the capability to conduct hydraulic conductivity tests at any depth in earthen materials above the permanent water table. Such depths may range from zero to many meters below the ground surface. In addition, it is desirable to have adequate flow capacity for maintaining flow equilibrium in a wide range of soils. Clay and marl strata often have slow permeability, whereas sandy or gravelly soils often have high permeability and, therefore, a greater equilibrium flow rate.
Not infrequently, when clay or marl strata are at or near the surface, it is necessary to prepare a hole through such strata into underlying layers having adequate permeability for receiving septic tank fluids and the like, whereby a tract of land may be developed by building single-family homes thereon.
Another matter of developing concern is the disposal of urban area rainwater into the ground in order to maintain the water table. With such large areas in urban areas and suburban areas being covered with roofs, parking lots, sidewalks, streets, and highways, there is very little opportunity for rainwater to be absorbed into the ground. It is instead gathered into storm sewers for transport into the nearest lake, river, or ocean, thereby bypassing underground strata that are pervious enough to water to receive and transport the wasted rainwater.
Prior art inventions that utilize a float system alone do not provide a mechanical advantage ratio, thereby limiting testing to relatively shallow depths. Inventions utilizing the marriotte tube principle to establish a constant water level are also limited to relatively shallow depths of testing.
A buoyant force is provided by a float in accordance with Archimedes's Principle which states that the buoyant force on a body immersed in a fluid is equal to the weight of the fluid displaced by that body. The displacement volume of any float of practical geometric shape that can fit in a small-diameter borehole is relatively small; therefore, the depth at which such a float can provide throttling of a valve by direct buoyant force alone is limited to relatively shallow depths and small flow rates.
There is accordingly a need for an apparatus that is sufficiently rugged and versatile to measure hydraulic conductivities of soils inside a borehole at a variety of depths above the water table, ranging from shallow to deep. None of the prior art apparatuses having a float utilize a magnifying means, such as a lever arm, to increase the available force for shutting off the flow of water into the apparatus.
There is also a need for a device that can be used inside a borehole, wherein the device is subject to being struck by falling soil particles and debris, without contamination by such particles and debris through the air vent hole at its top or through water outlets at its bottom.